“[w]hen a nation is at war, many things that might be said in times of peace are such a hindrance to its effort that their utterance will not be endured so long as men fight, and that no Court could regard them as protected by any constitutional right.” Schenck v. United States (1919)

"In 1969, Schenck was largely overturned by Brandenburg v. Ohio, which limited the scope of speech that the government may ban to that directed to and likely to incite imminent lawless action (e.g. a riot)." - Wikipedia